Our overall objective is to understand the factors controlling oxygen delivery to the fetus-in-utero. This includes factors affecting placental respiratory gas transfer, control of fetal cardiac output and factors affecting oxygen exchange in fetal tissues. Individual studies include: 1) determination of the relation of fetal oxygen consumption to the PO2 of fetal arterial blood, 2) derermination of the placental diffusing capacity in the chronically prepared unanesthetized sheep, 3) development of a mathematical model of the time course of PO2 changes in the fatal circulation, 4) determination of the effects of maternal hypoxia on fetal survival, 5) determination of the rate of uptake and elimination of CO in maternal and fetal blood as a function of the level of CO in inspired air, 6) determination of the relation of CO levels of muscle, carboxymyoglobin, to that of the blood, carboxyhemoglobin, for the mother and fetus 7) determination of the role of hydrostatic pressures in maternal and fetal blood vessels in affecting transplacental water movements, 8) determination of the role of osmotic pressures in maternal and fetal placental blood vessels in affecting transplacental water movements, 9) determination of the relation of fetal extracellular fluid volume to total fetal blood volume, 10) determination of the fetal mean systemic pressure, 11) determination of the relation of mean systemic pressure to fetal blood volume, 12) determination of fetal venous return curve as a function of right atrial pressure, 13) determination of fetal mean systemic pressure in a chronically prepared unanesthetized fetus.